Adjusted Bending Design Value for Lumber
Easywoodadjustment-factorsallowable-stress
A sawn lumber reference bending design value is Fb = 1,200 psi. The applicable load-duration factor is CD = 1.15 and the wet-service (moisture) factor is CM = 0.85; all other applicable bending adjustment factors equal 1.0. What is the adjusted bending value Fb′ = Fb·CD·CM?
- A1,380 psi
- B1,020 psi
- C1,173 psi
- D2,400 psi
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Answer: C. 1,173 psi
Adjustment factors multiply: Fb′ = 1,200 × 1.15 × 0.85 = 1,380 × 0.85 = 1,173 psi. 1,380 psi applies only CD and forgets the moisture reduction. 1,020 psi applies only CM and forgets the duration increase. 2,400 psi adds the factors (1.15 + 0.85 = 2.00) instead of multiplying them.
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